Field of the Invention
The invention pertains to the field of variable compression ratio systems. More particularly, the invention pertains to a variable compression ratio piston system for an engine.
Description of Related Art
Variable compression ratio (VCR) systems are known in the art. A compression ratio, as used herein, is the ratio of the volume of the cylinder chamber, or combustion chamber in the case of an engine, at its largest capacity to the volume at its smallest capacity. VCR systems for internal combustion engines are intended to be able to change the compression ratios of the pistons in their respective engine cylinders on the fly. This allows for increased fuel efficiency by varying the compression ratios in response to varying loads on the engine during operation. While VCR engine research goes back several decades and many automobile manufacturers are currently working on VCR engine designs, no current commercially-available automobiles have a VCR engine. The mechanical complexity and difficulty in controlling the system parameters to provide the desired improvement have thus far prevented commercialization of this technology in automobiles.
U.S. Pat. App. Pub. No. 2010/0163003, entitled “Electrohydraulic Device for Closed-Loop Driving the Control Jack of a Variable Compression Ratio Engine” by Rabhi and published Jul. 1, 2010, discloses an electrohydraulic device for controlling the compression ratio of a variable compression-ratio engine. In a first embodiment, two electrovalves are provided per control jack at an inlet and an outlet, each electrovalve being furnished with a check valve. In a second embodiment, a single electrovalve is provided and includes an electrically-controlled spool with two inlets and two outlets. In a third embodiment, a single two-way electrovalve is provided. The electrovalve is capable of opening and closing sufficiently rapidly to allow the movement of the control rack only for a few degrees of angular movement of the crankshaft. It should be noted that one of the positions seems to allow recirculation between the upper chamber and the lower chamber of the control jack.
U.S. Pat. App. Pub. No 2009/0320803, entitled “Control Method for a Variable Compression Actuator System” by Simpson and published Dec. 31, 2009, discloses a control system for an adjustment device for a variable compression ratio engine comprising: a jack head, a jack piston, a sprocket wheel, a movable transmission member, and a control valve. The jack piston is received within a chamber of the jack head defining first and second fluid chambers. The control valve controls the flow of fluid between the first and second fluid chambers. Based on the position of the control valve, fluid flows from the first fluid chamber to the second fluid chamber or vice versa, moving the control rack connecting the jack piston to the sprocket wheel. Reciprocating motion of the sprocket wheel adjusts the position of the cylinder of the engine.
The above-mentioned references are hereby incorporated by reference herein.
FEV, Inc. (Auburn Hills, Mich.) manufactures a two-step variable compression ratio (VCR) system. The FEV-developed 2-step VCR mechanism induces small variations in the rod length that are achieved by using the gas and mass forces for actuation. A compression ratio that is variable in two steps from 14:1-17:1 in the case of a commercial diesel version is thereby achieved. This ensures rapid and accurate actuation without the use of an expensive power actuator. Versions of the system are available for both gasoline and diesel engines and can be applied to almost all existing engines with bore diameters as low as 70 mm. In addition to increased engine efficiency, the system also offers emissions-related benefits, depending on whether applied to gasoline or diesel engines. Other potential benefits include improved cold startability and the potential to optimize performance while utilizing alternative fuels. The system can be integrated into existing engine designs due to a carry-over piston and pin design.